Controlled oxidation of iron nanoparticles in chemical vapour synthesis

Enteric-coated formulations can delay the release of drugs until they have passed through the stomach. However, high concentration of drugs caused by rapidly released in the small intestine leads to the intestinal damage, and frequent administration would increase the probability of missing medication and reduce the patient compliance. To solve the above-mentioned problems, aspirin-loaded enteric-coated sustained-release nanoparticles with core–shell structure were prepared via one-step method using coaxial electrospray in this study. Eudragit L100-55 as pH-sensitive polymer and Eudragit RS as sustained-release polymer were used for the outer coating and inner core of the nanoparticles, respectively. The maximum loading capacity of nanoparticles was 23.66 % by changing the flow rate ratio of outer/inner solutions, and the entrapment efficiency was nearly 100 %. Nanoparticles with core–shell structure were observed via fluorescence microscope and transmission electron microscope. And pH-sensitive and sustained drug release profiles were observed in the media with different pH values (1.2 and 6.8). In addition, mild cytotoxicity in vitro was detected, and the nanoparticles could be taken up by Caco-2 cells within 1.0 h in cellular uptake study. These results indicate that prepared enteric-coated sustained-release nanoparticles would be a more safety and effective carrier for oral drug delivery.     

Superchiral Pd3L6 Coordination Complex and Its Reversible Structural Conversion into Pd3L3Cl6 Metallocycles

Large, non‐symmetrical, inherently chiral bispyridyl ligand L derived from natural ursodeoxycholic bile acid was used for square–planar coordination of tetravalent Pd^II, yielding the cationic single enantiomer of superchiral coordination complex 1 Pd₃ L ₆ containing 60 well‐defined chiral centers in its flower‐like structure. Complex 1 can readily be transformed by addition of chloride into a smaller enantiomerically pure cyclic trimer 2 Pd₃ L ₃Cl₆ containing 30 chiral centers. This transformation is reversible and can be restored by the addition of silver cations. Furthermore, a mixture of two constitutional isomers of trimer, 2 and 2′ , and dimer, 3 and 3′ , can be obtained directly from L by its coordination to trans‐ or cis‐N‐pyridyl‐coordinating Pd^II. These intriguing, water‐resistant, stable supramolecular assemblies have been thoroughly described by ¹H DOSY NMR, mass spectrometry, circular dichroism, molecular modelling, and drift tube ion‐mobility mass spectrometry.     

Determination of the glass transition temperature of latex films: Comparison of various methods

The glass transition temperature (T_g) for two latices with different styrene/butadiene compositions was determined by the thermal SPM probe resonance frequency method. The results were compared with the T_g values obtained by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), process rheometer (PR) and thermo-mechanical analyzer (TMA) measurements. The T_g values detected by the thermal SPM method agreed well with the T_g values obtained by DSC and calculated by the Fox–Flory equation. DMA, on the other hand, showed a significantly higher T_g value for both latices than those obtained from theoretical calculations, the thermal SPM method and DSC. The T_g obtained from the PR curve was slightly higher for the latex with a low styrene content, whereas good agreement was obtained with the thermal SPM data for the latex with a high styrene content. The glass transition temperature determined by TMA agreed fairly well with the thermal SPM data for the latex with the low styrene content, whilst the value of T_g for the second latex was much less than those obtained by the other methods. The thermal SPM method detects changes in thermal behavior (thermal diffusivity, heat capacity) during heating of the latex films rather than changes in the mechanical properties. Information about the sample history could be seen in the thermal SPM curves, which was further associated with the degree of latex film formation, especially when the roughness of the films was taken into consideration.     

Thermal and topographical characterization of polyester- and styrene/acrylate-based composite powders by scanning probe microscopy

The thermal properties of two conventional polyester-based toners and a chemically prepared styrene/acrylate toner with different thermal histories were studied by scanning probe microscopy (SPM) and differential scanning calorimetry (DSC). The thermal transition temperatures detected by SPM agreed with the results of the DSC measurements. The validity of SPM for detecting thermal transitions was further confirmed by studying two amorphous reference polymers with different glass transition points (T_g) and three crystalline reference polymers with different melting points (T_m). When the toner sample was heated by the SPM probe above the glass transition temperature of the toner powder (T_probe > T_g), changes occurred in the surface topography and roughness causing different levels of local sintering of the particles. A set of roughness parameters calculated from the SPM image data were used to quantify the most essential features of toner surfaces. Environmental scanning electron microscopy (ESEM) was used to study the penetration depth of heat dissipated by the SPM probe. The probe-annealing was compared with oven-annealing in order to establish the effect of thermal history on the thermal properties of the materials.     

Comparison of Elemental Blood Analysis in Intact and Dry Samples: Porous Membranes as a New Sampling Format

Moscow University Chemistry Bulletin - The possibility of using dry blood samples on porous glass fiber membrane carriers (PGMCs) for the quantitative elemental analysis of blood using the method...     

Isomerism of [64Cu-NOTA-Bn]-labeled radiotracers: separation of two complex isomers and determination of their interconversion energy barrier using ion pair chromatography

The model complex [(64)Cu((S)-p-NH(2)-Bn-NOTA)](-) ([(64)Cu]1) was used to study the isomerism of [(64)Cu-NOTA-Bn]-labeled radiotracers. Two complex isomers [(64)Cu]1a and [(64)Cu]1b, which were formed at a ratio of 1:9 during the complexation of [(64)Cu]Cu(2+) with (S)-p-NH(2)-Bn-NOTA, were separated using ion pair chromatography. To study the interconversion, the nonradioactive complex isomers Cu1a and Cu1b were separated and thermally treated at 90 °C in both ammonium acetate solution and deionized water. A faster interconversion rate was observed for both isomers with lower concentrations of ammonium ions. At the end of reaction, the thermodynamic Cu1a to Cu1b equilibrium ratio was 6:94. The particular energy barriers of the interconversion for Cu1a and Cu1b were 130 kJ mol(-1) and 140 kJ mol(-1). Spectrophotometric measurements with Cu1a and Cu1b revealed two isomers adopting different geometrical configurations.     

Low-cost reduced graphene oxide-based conductometric nitrogen dioxide-sensitive sensor on paper

The fabrication concept for a low-cost sensor device using reduced graphene oxide (rGO) as the sensing material on a porous paper substrate is presented. The sensors were characterized using conductivity and capacitance measurements, atomic force microscopy and X-ray photoelectron spectroscopy. The effects of different reducing agents, graphene oxide (GO) flake size and film thickness were studied. The sensor was sensitive to NO₂, and devices based on a thin (10-nm) hydrazine-reduced GO layer had the best sensitivity, reaching a 70 % reduction in resistance after 10 min of exposure to 10 ppm NO₂. The sensitivity was high enough for the detection of sub-parts per million levels of NO₂. Desorption of gas molecules, i.e. the recovery of the sensor, could be accelerated by UV irradiation. The structure and preparation of the sensor are simple and up-scalable, allowing their fabrication in bulk quantities, and the fabrication concept can be applied to other materials, too.

Quantitative determination of acetylcholine in microdialysis samples using liquid chromatography/atmospheric pressure spray ionization mass spectrometry

A fast, simple and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the determination of acetylcholine in rat brain microdialysis samples. The chromatographic separation was achieved in 3 min on a reversed-phase column with isocratic conditions using a mobile phase containing 2% (v/v) of acetonitrile and 0.05% (v/v) of trifluoroacetic acid (TFA). A stable isotope-labeled internal standard was included in the analysis and detection was carried out with a linear ion trap mass spectrometer using selected reaction monitoring (SRM). Analyte ionization was performed with an atmospheric pressure chemical ionization (APCI) source without applying discharge current (atmospheric pressure spray ionization). This special ionization technique offered significant advantages over electrospray ionization for the analysis of acetylcholine with reversed-phase ion-pairing chromatography. The lower limit of quantification was 0.15 nM (1.5 fmol on-column) and linearity was maintained over the range of 0.15-73 nM, providing a concentration range that is significantly wider than that of the existing LC/MS methods. Good accuracy and precision were obtained for concentrations within the standard curve range. The method was validated and has been used extensively for the determination of acetylcholine in rat brain microdialysis samples.     

A novel particle sampling system for physico-chemical and toxicological characterization of emissions

Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency.